Computer Simulation of Zirconium-Hafnium Separation by Countercurrent Extraction

Abstract

In carrying out research and development on an improved method for production of reactor-grade zirconium oxide, the Bureau of Mines has prepared a computer program capable of accurately predicting the stage-by-stage performance of a multistage countercurrent solvent extraction system for separation of zirconium from hafnium using a tertiary amine extractant. The results were used to plan laboratory experiments using a multistage countercurrent mixer-settler unit. The number of extractor stages, number of scrubber stages, feed solution concentrations, scrubber solution concentration, feed flow, scrubber flow, and organic-phase flow are the significant variables. The computer simulation indicates the effects of changes in the pertinent variables and makes it possible to locate the best combination of variables without a prohibitively large number of time-consuming experiments.     

The dynamic response of a multiple-mixer column to flow rate disturbances

The paper presents a dynamic model of a multiple-mixer solvent extraction column, with backmixing effects and non-equilibrium stages, which allows the concentration response to be predicted following changes in the flow rates of the input feed or input solvent streams. The model is a development of earlier work[1] which considered the response to input concentration changes.Typical dynamic response results have been computed using steady state parameters determined experimentally for a 23 stage column operating on acetic acid/water/methyl isobutylketone. Some experimental results on the response of the raffinate concentration to step changes in the inlet feed and solvent streams are also given.     

Extraction equilibria of penicillin G in four different types of organic solvent systems

Equilibrium experiments for physical and reactive extraction of penicillin G were carried out with varying pH, overall penicillin concentration and overall amine concentration in liquid–liquid extraction systems with four different types of organic solvents, i.e. amphiprotic solvent, hydrogen-bond donor solvent, hydrogen-bond acceptor solvent, and nonpolar organic solvent. Also, physical and reactive extraction equilibrium models were suggested to find the appropriate equilibrium model for each organic solvent type. By comparison between the experimental data and the calculated results from the extraction equilibrium models, the most probable physical and reactive extraction equilibrium models were determined. The physical extraction equilibrium models for all types of the organic solvents except for nonpolar organic solvent reflected solute–solvent interaction, while the reactive extraction equilibrium models were dependent on the organic solvent type.     

丁酮-水共沸物系的萃取分离

采用液液萃取进行丁酮-水共沸物系的分离。测定了三元体系丁酮-水-（1-乙基-3-甲基咪唑醋酸盐）的液液平衡,采用NRTL活度系数方程对液液平衡数据进行回归得到组分间的二元交互作用参数。利用流程模拟软件ChemCAD进行了以离子液体为萃取剂的液液萃取过程的模拟,研究了理论板数、溶剂比（萃取剂摩尔流量和原料摩尔流量的比值）对萃取过程的影响,通过灵敏度分析,获得了优化的操作参数。在最适宜操作条件下,丁酮的摩尔分数可达0.999 4,离子液体经过回收能够直接循环使用。     

Liquid Emulsion Membrane (LEM) Process for Vanadium (IV) Enrichment: Process Intensification

Abstract

A liquid emulsion membrane (LEM) system for vanadium (IV) transport has been designed using di‐2‐ethylhexyl phosphoric acid (D2EHPA), dissolved in n‐dodecane as carrier. The selection of extractant, D2EHPA, was made on the basis of conventional liquid‐liquid extraction studies. The work has been undertaken by first carrying out liquid‐liquid extraction studies for vanadium (IV) to get stoichiometric constant (n), and equilibrium constant (K_ex), which are important for process design.

Transport experiments were carried out at low vanadium (IV) concentration (ppm level). The studies on liquid emulsion membrane included i) the influence of process parameters i.e. feed phase pH, speed of agitation, treat ratio, residence time and ii) emulsion preparation study i.e., organic solvent, extractant concentration, surfactant concentration, internal strip phase concentration. When the strip phase concentration was 2 mol/dm³ (H₂SO₄) and feed phase pH 3 better extraction of vanadium was obtained. Higher V_m/V₁ gave higher extraction of vanadium (IV). A simplified, design engineer friendly model was developed.     

亚临界水萃取植物精油的模型

Mechanisms that control the extraction rate of essential oil from Zataria multiflora Boiss. (Z. multiflora) with subcritical water (SW) were studied. The extraction curves at different solvent flow rates were used to determine whether the extractions were limited primarily by the near equilibrium partitioning of the analyte between the matrix and solvent (i.e. partitioning thermodynamics) or by the rates of analyte desorption from the matrix (i.e. ki-netics). Four simple models have been applied to describe the extraction profiles obtained with SW: (1) a model based solely on the thermodynamic distribution coefficient KD, which assumes that analyte desorption from the ma-trix is rapid compared to elution; (2) one-site kinetic model, which assumes that the extraction rate is limited by the analyte desorption rate from the matrix, and is not limited by the thermodynamic (KD) partitioning that occurs dur-ing elution; (3) two-site kinetic model and (4) external mass transfer resistance model. For SW extraction, the thermodynamic elution of analytes from the matrix was the prevailing mechanism as evidenced by the fact that ex-traction rates increased proportionally with the SW flow rate. This was also confirmed by the fact that simple re-moval calculations based on determined KD (for major essential oil compounds) gave good fits to experimental data for flow rates from 1 to 4 ml•min－1. The results suggested that the overall extraction mechanism was influenced by solute partitioning equilibrium with external mass transfer through liquid film.     

Cycling Zone Adsorption: Variable-Feed Mode of Operation

Abstract

Relatively large separations are possible using a single cycling zone adsorption column when operated with product recycle. Such a recycle may cause a large cyclic step-change in feed concentration, resulting in significant differences in alternating product stream concentrations. It is concluded that such a “variable-feed mode of operation” may allow the separation of compounds whose solid—fluid equilibrium distribution coefficients are only slightly affected by changes in a thermodynamic potential, or compounds which are difficult to separate by classical techniques such as distillation or extraction. It will also be apparent that the “variable-feed mode of operation” of a single zone (column) produces separations that could only be previously developed by a number of constant feed concentration zones operating in a series. Theoretical and experimental studies show that longitudinal diffusion is the primary cause of effluent concentration profile distortion, limiting the duration of peak product concentration flow.     

EXTRACTION OF COPPER BY LIX65N IN A VESSEL AND A MULTI-STAGE COLUMN UNDER STIRRED CONDITIONS

ABSTRACT

The extraction experiments of copper from aqueous solutions of copper sulfate by LIX65N-kerosene solutions were carried out at 25^°C in liquid-liquid dispersions. Both reaction rates of the forward and backward extractions were obtained in a stirred vessel, being combined with the equilibrium data. For a multistage column in continuous operation, the holdup data of the dispersed organic phase were correlated with the stirring speed, flow rates and LIX65N concentration. It was found that the extracted fraction of copper in the multi-stage column can be predicted from a stage-to-stage calculation using the extraction kinetics and the holdup obtained in the present work.     

Prediction of Concentration Profiles in an L‐Shaped Pulsed Extraction Column

The L‐shaped extraction pulsed plate column is believed to be able to perform under operating conditions between those of the vertical and the horizontal pulsed plate columns. It has an extraction efficiency similar to the vertical pulsed plate column. Here, the mass transfer performance of this novel column type was investigated and the application of three different models, i.e., the plug flow, the axial dispersion, and the back flow models, was evaluated to predict the solute concentration profile along the column length. The water‐acetone‐n‐butyl acetate and the water‐acetone‐toluene systems were used. The influence of the operational parameters on the height of the mass transfer unit and the back flow coefficients was evaluated using the back flow model. New correlations were proposed to predict the height of the mass transfer unit along with the back flow coefficients in each phase, which were in satisfactory agreement with the experimental data.     

Solvent extraction of uranium from acidic sulfate media by Alamine® 336: computer simulation and optimization of the flow‐sheets

BACKGROUND: A series of nine conventional and non‐conventional flow‐sheets have been considered for the recovery of uranium from acidic sulfate solution by liquid–liquid extraction with 0.146 mol L^?1 Alamine^® 336 in kerosene modified with 5% w/w 1‐tridecanol and stripping with a 199 g L^?1 Na₂CO₃ solution. The reference flow‐sheet was a classical counter‐current configuration with four mixers–settlers in the extraction stage and three mixers–settlers in the stripping stage. The others flow‐sheets possessing a total of eight mixers–settlers are unusual combined solvent extraction flow‐sheets with one or two independent extraction stripping loops and with one or two feed inlets. RESULTS: The configuration of the flow‐sheets strongly influences the extraction performance of the process depending on the working conditions (feed, stripping and solvent flow rates). The presence of two independent extraction–stripping loops may allow the delay of the saturation phenomenon encountered in the conventional flow‐sheet and thus, to operate at higher feed flow rates without loss of performance, as far as the residual fraction in the raffinate and the concentration factor in the stripping solution are concerned. Furthermore, the presence of a modification in the non‐conventional flow‐sheets with two independent extraction–stripping loops and two feed inlets leads to interesting configurations for uranium recovery from less concentrated solutions, such as heap leach solutions. CONCLUSION: The use of non‐conventional flow‐sheets is interesting as it allows the process of uranium (VI) recovery by liquid–liquid extraction to be improved. Copyright © 2009 Society of Chemical Industry     

Evolution of asphaltene floc size distribution in organic solvents under shear

A mathematical model was developed on the basis of population balance to analyze experimental data on asphaltene floc size distribution in a coagulating suspension. Experiments were carried out in a Couette device under a laminar flow condition. Floc size distributions were measured on-line using optical microscopy and image analysis. The aggregation behavior of asphaltenes was investigated by monitoring the size distribution of flocs for various intensities of agitation (i.e., shear rate, G), solvent composition (i.e., ratio of toluene to n-heptane in the solution, T:H) and particle contents (i.e., volume fraction of particles, ?). The results showed that (i) the floc size distribution can be predicted using a population balance approach, (ii) a steady-state mean floc size is reached for a given shear rate, and (iii) this steady-state floc size increases as ? is increased or T:H is reduced. The relative rates of shear-induced aggregation and fragmentation determine the steady-state size distribution. Similar floc size distributions were obtained at steady state for various shear rates, indicating that the width of the size distribution is independent of shear. However, the experimental observations indicate that the steady-state floc size distribution depends on asphaltene concentration and solvent composition.     

Extraction of phenols: Ii. distribution data for binary and multicomponent mixtures of phenols,countercurrent extraction performance and model validation

The distribution of binary mixtures of phenol with o-, m- or p-cresol between aqueous solutions of NaOH and toluene or methyl-isobutyl-ketone (MIBK) was investigated. A mathematical model of the distribution was formulated and its parameters were evaluated for each phenol/cresol/solvent combination. The extraction of phenolics from a coal tar fraction with aqueous solutions of sodium phenates was carried out in a countercurrent cascade of four equilibrium stages. The back extraction of phenolics from the aqueous extract was carried out as a triple extraction with pure solvent. A mathematical simulation of the multicomponent, multistage experiments was realized with the DOOM algorithm using an extension of the equilibrium model, formulated for binary mixtures.     

管式反应器合成乙二醇单乙醚工艺的模拟研究

为了开发新的乙氧基化工艺,提出和建立了三段管式反应器中试装置,用于乙醇乙氧基化反应合成乙二醇单乙醚(EGMEE)的模型开发和实验研究,并在Aspen Plus软件平台上开展了装置运行的模拟研究。考察了环氧乙烷(EO)加料位置、进料流量、醇烷比和换热方式等关键操作条件对环氧乙烷转化率、目标产物选择性及反应器热点温度的影响规律,得到优化的操作模式和操作参数。研究表明:管式反应器内反应和换热呈现复杂的耦合行为,沿管EO浓度分布是影响原料转化率、乙二醇单乙醚选择性、反应热移出和装置安全性的关键因素,采用EO多段加料和反应器多段冷却是提高装置稳定性和安全性的重要措施。     

Liquid–liquid equilibrium extraction of ethanol with mixed solvent for bioethanol concentration

The extraction of ethanol with the solvents of aldehydes mixed with m-xylene was studied for the bioethanol concentration process.Furfural and benzaldehyde were selected as extraction solvents,with which the solubility of water is small,expecting large distribution coefficient of ethanol.The liquid–liquid two-phase region was the largest with m-xylene solvent,followed by benzaldehyde and furfural.The region of two liquid–liquid phase became larger with the mixed solvent of m-xylene and furfural than that with furfural solvent.The NRTL model was applied to the ethanol–water–furfural–m-xylene system,and the model could well express the liquid–liquid equilibrium of the system.For any solvent used in this study,the separation selectivity of ethanol relative to water decreased as the distribution coefficient of ethanol increased.The separation selectivity with m-xylene was the largest among the employed solvents,but the distribution coefficient was the smallest.The solvent mixture of furfural and m-xylene showed relatively high distribution coefficient of ethanol and separation selectivity,even in the higher mass fraction of m-xylene in the solvent phase.The ethanol extraction with a countercurrent multistage extractor by a continuous operation was simulated to evaluate the extraction performance.The ethanol content could be concentrated in the extract phase with relatively small number of extraction stages but low yield of ethanol was obtained.     

煤气化废水处理过程瓶颈及改进措施分析

对煤气化废水处理过程进行的全流程模拟结果进行了瓶颈分析,针对流程中存在的CO2残留量高导致的铵盐结晶和萃取脱酚效率低等问题,分析了各种可能的改进措施。结果表明,残留CO2主要是以离子态存在的,增加汽提塔的塔板数和调酸降低pH值都不能经济有效地降低CO2残留量,适当措施是提高汽提塔操作压力;通过增加现有脱酚萃取剂二异丙醚流量、萃取级数或降低pH值以使废水酚残留量降至400 mg/L以下都不具备工业可行性;而采用甲基异丁基甲酮(M IBK)作萃取剂可达到这一要求,并将废水中COD残留量降至4 000 mg/L左右,达到生化处理的进水要求。     

Simulation and analysis of multi-stage centrifugal fractional extraction process of 4-nitrobenzene glycine enantiomers☆

Based on the interfacial ligand exchange model and the law of conservation of mass, the multi-stage enantioselective liquid–liquid extraction model has been established to analyze and discuss on multi-stage centrifugal fractional extraction process of 4-nitrobenzene glycine (PGL) enantiomers. The influence of phase ratio, extractant concentra-tion, and PF6?concentration on the concentrations of enantiomers in the extract and raffinate was investigated by experiment and simulation. A good agreement between model and experiment was obtained. On this basis, the influence of many parameters such as location of stage, concentration levels, extractant excess, and number of stages on the symmetric separation performance was simulated. The optimal location of feed stage is the middle of fractional extraction equipment. The feed flow must satisfy a restricted relationship on flow ratios and the liquid throughout of centrifugal device. For desired purity specification, the required flow ratios decrease with extractant concentration and increase with PF6?concentration. When the number of stages is 18 stages at extractant excess of 1.0 or 14 stages at extractant excess of 2.0, the eeeq (equal enantiomeric excess) can reach to 99%.     

Counter-Current Carbon Dioxide Purification of Partially Deacylated Sunflower Oil

A liquid carbon dioxide counter-current fractionation method was developed to remove by-product fatty acid propyl esters (FAPEs) from the reaction mixture after the partial deacylation of sunflower oil. The fractionation column was 1.2 m long and separations were done at 25 °C and 8.27 MPa. Several solvent to feed ratios (S:FR) (i.e., 7.6, 15.2, 30.3 and 60.6 g/g) and feed rates (FR) (i.e., 1, 2, 2.5, 3 and 4 mL/min) at a constant S:FR of 15.2 were examined. Raffinate purity (i.e., percentage glycerides) and extract purity (i.e., percentage FAPEs) were both monitored. Percentage glycerides in both the raffinate and the extract increased with S:FR. The raffinate contained ca. 83, 97, 100 and 100% glycerides at S:FRs of 7.6, 15.2, 30.3 and 60.6, respectively. The percentage glycerides in the extracts were ca. 3, 4, 8 and 17%, respectively. With the S:FR held constant at 15.2, the raffinate purity peaked at ca. 99% glycerides at a FR of 2.5 mL/min and the extract at this FR contained ca. 96% FAPEs. The optimal S:FR and FR determined from the experimental assays was applied to large batches in both a semi-continuous feed mode, and later in a continuous feed mode, which gave raffinates of 99.3 and 98.1% glycerides, respectively, and extracts of 97.3 and 97.2% FAPEs, respectively. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name USDA implies no approval of the product to the exclusion of others that may also be suitable.     

Use of the SEPHIS-MOD4 Program for Modeling the Purex and Thorex Solvent Extraction Processes

Abstract

The SEPHIS-MOD4 computer program simulates solvent extraction in the Purex and Thorex processes. The program employs simple mass balance equations to describe the movement of solutes through the idealized mixer-settler stages which are used in the model. These differential mass-balance equations are integrated by an iterative scheme that allows the user to observe transient changes and the resulting steady state profile in the mixer-settler system. Correlations describe the equilibrium concentrations in the aqueous and organic phases. Kinetic rate equations are used to simulate the reduction of plutonium by hydroxylamine nitrate and uranium(IV).

The value of the SEPHIS-MOD4 program lies primarily in its application to the design and testing of solvent extraction flowsheets. Given a set of operating conditions, the program can predict the solute concentration profile at steady state and during the approach to steady state. Changes in the operating conditions can be used to determine the influence of important system variables or to simulate the effects of a process upset.     

Studies on the Development of a Flow-Sheet for AHWR Spent Fuel Reprocessing Using TBP

The present paper describes the results of solvent extraction studies carried out in batch mode to collect data on distribution of uranium, plutonium, and thorium using 5% TBP in n-dodecane. Extraction studies are carried out from feed solutions having bulk thorium containing aluminum and fluoride ions in ～3.00–4.00 M nitric acid at concentration levels anticipated in feed solutions during Advanced Heavy Water Reactor (AHWR) spent fuel reprocessing. Studies are carried out under varied experimental conditions. Parameters such as organic to aqueous phase ratio during extraction, concentration of nitric acid for scrubbing co-extracted thorium from loaded organic phase etc., are studied in detail. Hydroxylamine nitrate is selected for reductive stripping of plutonium in preliminary studies. Reagent mixture containing 0.30 M HAN + 0.60 M HNO₃ and 0.20 M N₂H₄ is found to be optimum for plutonium partitioning. This paper also describes the extraction and stripping of uranium and plutonium in co-current mode. The extraction behavior of relevant fission products is studied from a simulated feed solution. A preliminary study on a few commercially available reducing agents is also included. These data are useful in developing a flow-scheme for the recovery of uranium and plutonium from spent fuel originating from AHWR.     

Supercritical fluid extraction from dried banana peel (Musa spp., genomic group AAB): Extraction yield, mathematical modeling, economical analysis and phase equilibria

Supercritical fluid extraction from dried banana peel (Musa spp., subgroup Prata, genomic group AAB, popularly known in Brazil as Enxerto) was studied. The aspects investigated were: overall extraction curve (OEC), mass transfer modeling of the yield curves, economical analysis of the process and phase equilibrium data for the pseudo-ternary system of banana peel extract, carbon dioxide and ethanol. The extraction operating conditions evaluated were: pressure ranging from 100 bar to 300 bar, temperature from 40 to 50 °C and constant solvent flow rate of 5.0 gCO₂/min. Experimental extraction data were correlated using three kinetic models based on mass transfer equations (logistic, diffusion and Esquível models). Phase equilibrium measurements were performed using pressure from 64.9 bar to 239.9 bar and mass fraction of supercritical extract from 0.52 to 3.55 wt%. Yield results ranged from 0.6 to 6.9% d.b. (dry basis). The lowest deviation between experimental and correlated data was obtained by the Logistic model, except for the curve at 300 bar and 40 °C which was best represented by the Esquível model. The economical analysis identified the possibility to apply the supercritical fluids to obtain extracts from banana peel in an industrial scale. Phase equilibrium for the supercritical extract from banana peel with carbon dioxide modified by ethanol exhibited liquid-liquid, vapor-liquid (bubble point) and vapor-liquid-liquid phase transitions. A crossover phenomenon for the systems evaluated was observed for pressures between 200 bar and 240 bar, for both groups of assays, i.e., supercritical extraction and phase equilibrium.